The broad objective of this research is to determine characteristic properties of highly purified cardiac and smooth muscle alpha-actinin and tropomyosin both individually, and in combination with other myofibrillar proteins, in order to increase our understanding of the function of these two proteins and our knowledge of the cardiac and smooth muscle contractile systems. Specific objectives and methods of the proposed research include: (1) determination of the molecular size, amino acid composition, nature of natural subunits, and other molecular parameters of smooth muscle alpha-actinin and tropomyosin; (2) a thorough biochemical comparison of smooth muscle alpha-actinin and tropomyosin with the corresponding proteins isolated from cardiac and skeletal muscle; (3) study of the interaction of alpha-actinin (in both cardiac and smooth systems) with the other myofibrillar proteins, particularly actin and tropomyosin, in order to help clarify the biological roles of alpha-actinin and tropomyosin; and (4) determination of the exact location of alpha- actinin in the intercalated disc region and amorphous or Z-lattice filaments of cardiac muscle, and localization of alpha-actinin and tropomyosin in smooth muscle by antibody-binding, proteolytic dissection and selective extraction techniques coupled to electron microscopic experiments.